This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-206926, filed Jul. 7, 2000, the entire contents of which are incorporated herein by reference.
The present invention relates to a measuring method for obtaining, for example, the tilting center of a power roller for a toroidal type continuously variable transmission.
FIG. 13 shows a variator that constitutes a principal part of a double-cavity half-toroidal type continuously variable transmission 10. The transmission 10 comprises an input disc 12 and an output disc 13, which constitute a first cavity 11, and an input disc 12 and an output disc 13, which constitute a second cavity 14. A pair of power rollers 15 are provided between the input and output discs 12 and 13 of the first cavity 11. The outer peripheral surface of each power roller 15 is in contact with the respective traction surfaces T of the input and output discs 12 and 13. A pair of power rollers 15 are also provided between the input and output discs 12 and 13 of the second cavity 14.
Each power roller 15 is rotatably mounted on a trunnion 17 by means of a power roller bearing 16. The trunnion 17 is rockable around a trunnion shaft 18. The input discs 12 are rotatable integrally with an input shaft 20. The input shaft 20 is connected to a drive shaft 21 that is rotated by means of a drive source, such as an engine. The paired output discs 13 are connected to each other by means of a connecting member 22. An output gear 23 is provided on the connecting member 22. A loading cam mechanism 25 is located at the back of the input disc 12 of the first cavity 11. The rotation of the drive shaft 21 is transmitted to the input disc 12 by means of the loading cam mechanism 25. The rotation of each input disc 12 is transmitted to its corresponding output disc 13 through the power rollers 15. As the output discs 13 rotate, the output gear 23 rotates.
As shown in FIG. 7, each substantially hemispherical power roller 15 has toroidal surfaces 30 that touch the respective traction surfaces T of the input and output discs 12 and 13 and a reference surface 31 that extends at right angles to a central axis Q of the roller 15. Curvature centers OL and OR of the toroidal surfaces 30, which are situated bisymmetrically with respect to the central axis Q in a cross section of the power roller 15 along the central axis Q, are kept at a distance D from the central axis Q and a distance A from the reference surface 31 each. Each toroidal surface 30 is a convex surface with the curvature radius r. The toroidal surfaces 30 touch the respective traction surfaces T of the input and output discs 12 and 13 in a tiltable manner. Each traction surface T is a concave toroidal surface with a curvature radius Rt. In FIG. 7, OD designates the curvature center of the traction surface T.
If the curvature center OD Of the traction surfaces T of the discs 12 and 13 is deviated from the tilting center of each power roller 15, slipping is caused at contact portions between the power roller 15 and the discs 12 and 13. This slipping lowers the torque transmission efficiency, and rolling fatigue that is attributable to heating shortens the life of the variator. If the deviation between the respective positions of the curvature center OD and the tilting center of the power roller 15 is great, a contact ellipse along which the roller 15 and the discs 12 and 13 are in contact is deviated from the boundaries of the effective traction surfaces. In this case, excessive pressure acts on the boundaries between a part of the contact ellipse and the effective traction surfaces, thereby drastically shortening the rolling fatigue life. Thus, the aforesaid positional deviation also exerts a bad influence upon an appropriate pressure at the rolling contact portions between the power roller 15 and the discs 12 and 13.
For these reasons, it is to be desired that the power rollers 15 should be rotated synchronously and that the tilting center of each power roller 15 and the curvature center OD of the traction surfaces of the discs 12 and 13 should be made coincident while this transmission is driven. To attain this, the curvature radius of the toroidal surfaces 30 of the power roller 15 and the tilting center of the roller 15 must be accurately obtained so that the discs 12 and 13 and the roller 15 can be positioned accurately.
Thereupon, the toroidal surfaces 30 of each power roller 15 are measured. A shape measurer of the straight-moving type and a three-dimensional measurer are known measuring devices for the power rollers 15. An alternative measuring device is developed and described in Jpn. Pat. Appln. KOKOKU Publication No. 59-44561. This device comprises a rotatable spindle, a micrometer attached to the spindle, a probe to be in contact with a curved surface of a workpiece, etc. In this measuring device, the probe is kept in contact with the workpiece to measure the distance of separation of the workpiece surface from a predetermined circle or circular arc. This measuring device can obtain the curvature radius r of the toroidal surfaces 30, distance 2D between the curvature centers OL and OR, distance A from the reference surface 31 to the curvature centers OL and OR, deviation of shape from an imaginary toroidal surface obtained by approximation to a representative circle with the curvature radius r, tilting center of each power roller 15, etc.
Since each toroidal surface 30 has a narrow measurable region, it is subjected to representative circle approximation by computation based on measured values, its radius, curved surface shape error (distance of separation from the predetermined circle or circular arc), etc. are obtained, and the tilting center is obtained from those values. If each toroidal surface 30 that has a slight shape error xcex94r, such as deformation or waviness, which is caused when the power roller 15 is worked, is subjected to representative approximation, as shown in FIG. 8, therefore, there is a deviation or error between the curvature center OL of a normal shape E-F-G and a curvature center OLxe2x80x2 of an actual shape E-F-Gxe2x80x2. In consequence, an estimated position of the tilting center of the power roller 15 is inevitably subject to an error after the roller 15 and the discs 12 and 13 are assembled.
According to a known curved surface measuring method described in Jpn. Pat. Appln. KOKAI Publication No. 8-285506, the curvature radius and curvature center of a concave surface are measured by means of a plurality of reference spheres with different diameters and a cramping member. However, this method serves only to measure concave surfaces and cannot be applied to the measurement of convex surfaces such as toroidal surfaces of power rollers.
Accordingly, the object of the present invention is to provide a measuring method for a power roller, capable of easily measuring various data, such as the tilting center of a power roller for a toroidal type continuously variable transmission, with reduced errors.
In order to achieve the above object, according to the present invention, there is provided a measuring method for a power roller for a toroidal type continuously variable transmission, the power roller having a reference surface extending at right angles to the central axis thereof and toroidal surface in contact with traction surfaces of discs, the measuring method comprising: a process for obtaining an intersection between a first circular arc traced around a measuring point on the toroidal surface on one side by the extreme end of a segment with a length equal to the curvature radius of the traction surfaces and a second circular arc traced around a measuring point on the toroidal surface on the other side by the extreme end of the segment, in a cross section along the central axis of the power roller; a process for obtaining a plurality of intersections by repeating the process for obtaining the intersection for each of different measuring points on the toroidal surfaces; a process for selecting that one of the intersections which is situated nearest to the reference surface and concluding that the selected intersection is the tilting center of the discs; and a process for obtaining the distance from the tilting center to the reference surface.
According to the present invention, moreover, there is provided a method for measuring a toroidal surface of a workpiece, such as a power roller, the workpiece having a reference surface extending at right angles to the central axis thereof, the measuring method comprising a process for bringing the workpiece into a concave spherical surface of a jig with a curvature radius greater than that of the toroidal surface and obtaining the distance from the reference surface to the center of the concave spherical surface.
According to the present invention, furthermore, there is provided a method for measuring a toroidal surface of a workpiece, the workpiece having a reference surface extending at right angles to the central axis thereof, the measuring method comprising: a first process for bringing the workpiece into contact with a first concave spherical surface of a first jig with a curvature radius greater than that of the toroidal surface, thereby obtaining the distance from the reference surface to the center of the first concave spherical surface; a second process for bringing the workpiece into contact with a second concave spherical surface of a second jig with a curvature radius greater than that of the first concave spherical surface, thereby obtaining the distance from the reference surface to the center of the second concave spherical surface; a third process for bringing the workpiece into contact with a third concave spherical surface of a third jig with a curvature radius greater than that of the second concave spherical surface, thereby obtaining the distance from the reference surface to the center of the third concave spherical surface; and a process for calculating the curvature radius and curvature center of the toroidal surface in accordance with at least the individual distances obtained in the first to third processes and the respective known curvature radii of the first to third concave spherical surfaces.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.